Method of coating metal



Patented 1.... 12, 1931 2,067,216

UNITED. STATES PATENT OFFICE amnion or COATING METAL John SQThompson, Detroit, and Herman J. Lodeesen, Berkley, Mich assignors to The,

Patents Corporation, Detroit, Mich. No Drawing. Applicat'on August 19, 1936,"

' Serial No. 96,904 r 7 .Claims. (C1. 148-6) This invention relates to coating metal and The object of the present invention-is to provide more particularly it relates to an improvement in an intermediate treatment after the production methods by which a substantially integral coatof the chemical coat bymeans of a solution coning is produced by chemical means upon a metal taining the N02 radical and before the applica- 5 surface which is thereafter covered with a coat tion of the siccative coat, whereby thi bli e n 5 of paint, varnish, enamel or the like which dries under the siccative coat is minimized or' elimior hardens over the chemical coat and is herehated. I inafter referred to for brevity as a siccative coat. After the production of the chemical coat, the It is known that various'treatments will prosurface is customarily washed before the appliduce a substantially integral coat upon metal by cation of the siccative coat. In accordance with 1 chemical changes in the .surface of the metal I the Present i v n. the chemical 0094" 1S P which result in firmer adherence of a siccative e ab y r s d in the u ual manner and is then coat thereto than can be obtained by direct aptreated with a dilute solution of chromic acid, plication of the siccative coat upon bare metal. phosphoric acid or oxalic acid. Treatment with This has been practiced to a considerable extent, dilute solutions of other acids, with a few excep- 1 particularly with iron and steel, by the production tions such as nitric acid, reduces to some extent. on iron andsteel of a phosphate coating as a the blistering but not as effectively and satisfoundation or bond for paint or the like. Similar factorily as the acids named. A treatment in a phosphate coats may be produced upon zinc or dilute solution of nitric acid seems to increase 0 magnesium, and by somewhat similar treatments rather than decrease the blistering.

substantially insoluble salts of the-metals may The threeacids named above are preferred in be produced by treatment with organic acids in-. the-order in which they are named, the chromic cluding the dicarboxylic and hydroxy-dicarboxylic acid being decidedly preferable, phosphoric acid acids of the aliphatic series, and carboxylic acids being next in efliciency, -and oxalic adld being not 5 having ,but one carboxyl group, and sulphonic so desirable but still eifective to materially reduce acids of the aromatic series, particularly where the blistering. oxidizing agents and copper compounds or the like In the preferred form, the chromic acid solution are employed as accelerators. By proper manipis formed by introducing from 2 grams to ulation, such salt 'coatings can be produced not grams of c om a i i a gallon of W Fo only upon iron and zinc, but also upon tin, lead ordinary commercial purposes about 4 grams ofand copper. These various coatings, when formed chromic acid to a gallon of water is preferred, but so that they are firmly adherent and substanfairly good results may be obtained with a dilution tially integral coatings upon the metal, greatly as great as 2 grams in a gallon of water, and while increase the adherence of siccative coats to the a strength greater than 4 grams to a gallon of metal. Also proper chemical treatment produces water seems unnecessary, it seems to do little, if

oxide coats on substantially all metals, and siccaany, harm until 20 grams or over are used. tive coats'adhere to such oxide coats better than Stronger solutions of chromic acid are likely to to the bare metal. Similar increased adherence injure the chemical coat, and even with 20 grams may be secured on aluminum by a coating of lit'nto the gallon, undesirable yellow streaks develop, 40 ium aluminate or aluminum fluoride. The nialthough these streaks do not seem to affect the trous acid radical generally added to the soluadherence of the siccative coat. tions in the form of soluble nitrites such as so- It is preferable to employ the customary rinsing dium nitrite, generally facilitates the production after the production of the chemical'coat and of oxide coatings on metal and also the producbefore the use of the chromic acid rinse, so as to tion of integral salt coats of the kind described avoid contamination of the chromic acid rinse. above. These various bonding coats are here- No treatment is necessary after the chromic acid inafter referred to for brevity as chemical coats. rinse and before the application of the siccative While the adherence of siccative coats to the coating. If any subsequent rinsing takes place, metal is greatly increased by the bonding effect it should be with distilled water or at least with of a chemical coat, it has been found diflicult to water which does not contain lime, alkali or other avoid-blisters between the chemical coat and the material which may result in contaminating the siccative coat where the chemical coat has been chemical coat sufliciently to produce blisters. produced with the aid of the nitrous acid radical The length of A treatment in the chromic acid particularly when the finished surface is subrinse depends upon the strength of the solution 56 iected to humidity tests. employed, the condition of the work and the tememp oyed, 1 may be used hot in a solution having a strength normal caustic soda to neutralize g0 rinse water, methyl orange being th dic'ator. Where this rinse water is employedrover azphos phate chemical coat, it graduallybecomescon- .taminated with phosphates and is not effective where the phosphate builds up so that it-,reguire s more than four times as much alkali to'rieuti ali a given amount of solution with phenolphthalein samenamount ,of 5 Solution 1 with methyl orange as an--;indicator. -:About o ne. min ute treatmentin phosphori'c--acid rinse is ordinarily suffilng strength to that indicated above for the phosphoriczacid fsolution. j

The acid rinse to minimize or eliminate blisters under a siccative coat is particularly effective when employed .witha chemical coat produced by a .phosphatesolution containing the nitrous acid,-

radical N02; but-is alsoeffective with the other chemical.coatsmentioned above which .are obtained on metallic surfaces bymeansof-solutions containing the N02 radical. Also, while the most important use of the'method at the present time is in connection with coating iron or steel, it is also effective with the chemical coats produced upon other metals, as mentioned above.

It is understood that in the rinses of this invention other ingredients may be present besides the chromic, oxalic and phosphoric acids; for example, mixtures of any of these may be used, although substantially pure, dilute, aqueous solutions of these acids are preferably employed.

After the rinse of this invention the metallic surfaces are either air-dried or heat-dried before application of the siccative coat.

What we claim is:

1. 'The method which consists in forming on asurface of metal by means of a solution containoxalicacid rinse; employed, it, whicl i theldilut ej aci shouldbeused-hotin approximately corresp0nd- 4 i 1 acid perjgallon of water.

'metal surface carrying a chemical coating pro- .of substantially insoluble phosphates, on iron, steel, zinc, magnesium, tin, lead and copper, of a substantially insoluble salt of an acid in the group consisting of the dicarboxylic and hydroxy-dicarboigyli'qaci ds'gofgthe aliphaticsseries and car- 6 gabutoiia'carboiiyl group and sulphonic acids of the aromatic series, and, on which requires between cc. and /2 cc. tentli-. :-r'. aluminum, lithium aluminate and aluminum fluoride,,rinsing the chemical coat. with a substaritiallVpilredflute aqueous solution of an acid roum consist ing of chromic acid, phosphcri acid androxalic acid and mixtures thereof, an'd coverln'g gthei'riiised chemical coat with a e 'methodwliiiih consists in producing on a 15 metallic 'surface a phosphate-containing coating as an indicator than it does to neutralize-"the 1? by me'aQns'Tofi a solution containing the N02 radical.

and after. the coati the' coatedfsurfa'c' in chromic' a'cid.

3.. 'A... method' mace da "be ith] c l ii i"- rm s' a' chrorziic"'acid rinse,'of the strength 'of which the acid rinse is e A L Q-j mm .c soda to neutralizeflO cclof the s'olution,'methyl orange bein el ndibjefio 5. A" method in accordance with claini l in which .jthe acid rinse is a solution ofphosphoric' acid. requiring between EA cc.' and "cc; tenth normal caustic so'dato neutralize 10' cc..ofthe"solu- 7 tion, methyl orange being the; indicator, and re-' quiring not more'than'fo'ur times as much alkali to. neutralize a given amount of the solution with phenolphthalein as an indicator than with methyl orange as an indicator. 7

6. The method which comprises treating a 40 duced by theaction of a solution containing the N02 radical, with a substantially pure dilute aqueous solution of one of the group consisting of chromic acid, phosphoric acid, oxalic acid, and mixtures thereof.

'7. The method which comprises treating a surface of iron or steel carrying a chemical coating containing phosphate produced by the action of a solution containing the N02 radical, with a dilute aqueous solution of chromic acid.

JOHN S. THOMPSON.

HERMAN J. LODEESEN.

CERT FICATE OF wmw Patent No. 2,067,216.; [January-T lzgissv.

JOHN s. THOMPSON-T ET AL.

It is hereby certified that rrorappear 'inlthe' printed;pgcification o! the ab'ovgf numbered patent requiring Correction -as follows :"-TPeigeY-Z. .s Q column, .line 18 ,.-.,.c1 aim"2, str ike I opjtthewbrdSfjKfte v-tbc e'f dpgti zdope'ra tioh'" anqjhat-"the;fsaid" Letters Patennfs hou l d :bxi'fii ij r e i l, thei'eifi' thifl .tki-Ts.mifi.yf cciafifqr m'toftl gsf reqordf of the" :case in oh Henry Van Arsdale (Seal) 'Acting Commissioner of Patents. 

